Insulator oxide films, particularly silicon oxide films, have conventionally been made by methods such as thermal oxidation of silicon, physical vapor deposition and chemical vapor deposition, most typically chemical vapor deposition. However, chemical vapor deposition requires high temperatures, e.g., above 300° C., even with the aid of a plasma. Newer, lower temperature techniques, known as Chemical Fluid Deposition (CFD), are based on chemical deposition of the oxide films from a supercritical fluid solution have been developed.
U.S. Pat. No. 4,970,093 describes a method for depositing a film of a desired material on a substrate comprising dissolving at least one reagent in a supercritical fluid comprising at least one solvent. Either the reagent is capable of reacting with, or is a precursor of, a compound capable of reacting with the solvent to form the desired product, or at least one additional reagent is included in the supercritical solution and is capable of reacting with, or is a precursor of, a compound capable of reacting with the first reagent or with a compound derived from the first reagent to form the desired material. The supercritical solution is expanded to produce a vapor or aerosol and a chemical reaction is induced in the vapor or aerosol so that a film of the desired material resulting from the chemical reaction is deposited on the substrate surface. In an alternate embodiment, the supercritical solution containing at least one reagent is expanded to produce a vapor or aerosol which is then mixed with a gas containing at least one additional reagent. A chemical reaction is induced in the resulting mixture so that a film of the desired material is deposited.
U.S. Pat. No. 5,789,027 describes methods for depositing a film of material on the surface of a substrate by i) dissolving a precursor of the material into a supercritical or near-supercritical solvent to form a supercritical or near-supercritical solution; ii) exposing the substrate to the solution, under conditions at which the precursor is stable in the solution; and iii) mixing a reaction reagent into the solution under conditions that initiate a chemical reaction involving the precursor, thereby depositing the material onto the solid substrate, while maintaining supercritical or near-supercritical conditions. The invention also includes similar methods for depositing material particles into porous solids, and films of materials on substrates or porous solids having material particles deposited in them.
U.S. Pat. No. 6,541,278 describes a semiconductor substrate that is placed within a housing. By supplying organometallic complexes and carbon dioxide in a supercritical state into the housing, a BST thin film is formed on a platinum thin film, while at the same time, carbon compounds, which are produced when the BST thin film is formed are removed. The solubility of carbon compounds in the supercritical carbon dioxide is very high, and yet the viscosity of the supercritical carbon dioxide is low. Accordingly, the carbon compounds are removable efficiently from the BST thin film. An oxide or nitride film may also be formed by performing oxidation or nitriding at a low temperature using water in a supercritical or subcritical state, for example.
U.S. Pat. No. 6,716,663 describes a method wherein a semiconductor substrate is placed within a housing. By supplying organometallic complexes and carbon dioxide in a supercritical state into the housing, a BST thin film is formed on a platinum thin film, while at the same time, carbon compounds, which are produced when the BST thin film is formed, are removed. The solubility of carbon compounds in the supercritical carbon dioxide is very high, and yet the viscosity of the supercritical carbon dioxide is low. Accordingly, the carbon compounds are removable efficiently from the BST thin film. An oxide or nitride film may also be formed by performing oxidation or nitriding at a low temperature using water in a supercritical or subcritical state, for example.
Although these methods of chemical deposition form supercritical fluid solutions provide advantages over conventional deposition techniques, they can still be improved. In particular, faster reaction/deposition rates are desired. Also, providing a broader array of precursors and reagents would also be advantageous.